Hydraulic failure defines the recovery and point of death in water-stressed conifers
Brodribb, TJ and Cochard, H, Hydraulic failure defines the recovery and point of death in water-stressed conifers, Plant Physiology, 149, (January) pp. 575-584. ISSN 0032-0889 (2009) [Refereed Article]
This study combines existing hydraulic principles with recently developed methods for probing leaf hydraulic function to
determine whether xylem physiology can explain the dynamic response of gas exchange both during drought and in the
recovery phase after rewatering. Four conifer species from wet and dry forests were exposed to a range of water stresses by
withholding water and then rewatering to observe the recovery process. During both phases midday transpiration and leaf
water potential (Cleaf) were monitored. Stomatal responses to Cleaf were established for each species and these relationships
used to evaluate whether the recovery of gas exchange after drought was limited by postembolism hydraulic repair in leaves.
Furthermore, the timing of gas-exchange recovery was used to determine the maximum survivable water stress for each
species and this index compared with data for both leaf and stem vulnerability to water-stress-induced dysfunction measured
for each species. Recovery of gas exchange after water stress took between 1 and .100 d and during this period all species
showed strong 1:1 conformity to a combined hydraulic-stomatal limitation model (r2 = 0.70 across all plants). Gas-exchange
recovery time showed two distinct phases, a rapid overnight recovery in plants stressed to ,50% loss of leaf hydraulic
conductance (Kleaf) and a highly Cleaf-dependent phase in plants stressed to .50% loss of Kleaf. Maximum recoverable water
stress (Cmin) corresponded to a 95% loss of Kleaf. Thus, we conclude that xylem hydraulics represents a direct limit to the
drought tolerance of these conifer species.